Thermal Cycling Apparatus and Method for Providing Thermal Uniformity

ABSTRACT

An apparatus and method for rapid thermal cycling including a thermal diffusivity plate. The thermal diffusivity plate can provide substantial temperature uniformity throughout the thermal block assembly during thermal cycling by a thermoelectric module. An edge heater can provide substantial temperature uniformity throughout the thermal block assembly during thermal cycling.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 10/448,804filed May 30, 2003, which is incorporated herein by reference.

FIELD

The present teachings relate to thermal cycling of biological samples.Improvement in thermal cycling can be provided by a thermal diffusivityplate.

INTRODUCTION

In the biological field, thermal cycling can be utilized to provideheating and cooling of reactants in a reaction vessel. Examples ofreactions of biological samples include polymerase chain reaction (PCR)and other reactions such as ligase chain reaction, antibody bindingreaction, oligonucleotide ligations assay, and hybridization assay. InPCR, biological samples can be thermally cycled through atemperature-time protocol that includes melting DNA into single strands,annealing primers to the single strands, and extending those primers tomake new copies of double-stranded DNA. During thermal cycling, it isdesirable to maintain thermal uniformity throughout a thermal blockassembly so that different sample wells can be heated and cooleduniformly to obtain uniform sample yields. Uniform yields can providequantification between samples wells.

SUMMARY

According to various embodiments, an apparatus for thermally cyclingbiological samples can comprise a thermal block assembly for receivingthe biological sample; a thermoelectric module coupled to the thermalblock assembly; and a heat sink, wherein the heat sink is coupled to thethermoelectric module, wherein the heat sink comprises a base plate,fins, and a thermal diffusivity plate, and wherein the thermaldiffusivity plate comprises a different material than the base plate andfins, wherein the thermal diffusivity plate provides substantialtemperature uniformity to the thermal block assembly during thermalcycling.

According to various embodiments, an apparatus for thermally cyclingbiological samples can comprise a thermal block assembly for receivingthe biological sample; a thermoelectric module coupled to the thermalblock assembly; a heat sink; and a thermal diffusivity plate coupled tothe thermoelectric module and the heat sink, wherein the thermaldiffusivity plate is positioned between the thermoelectric module andthe heat sink, wherein the thermal diffusivity plate has a significantlygreater thermal diffusivity than the heat sink.

According to various embodiments, a method for thermally cyclingbiological samples can comprise contacting a thermoelectric module to athermal block assembly; heating the thermal block assembly, wherein thethermal block assembly is adapted for receiving the biological sample;and cooling the thermal block assembly, wherein the cooling comprisesdiffusing heat to a heat sink through a thermal diffusivity plate.

It is to be understood that both the foregoing general description andthe following description of various embodiments are exemplary andexplanatory only and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate various embodiments. In thedrawings,

FIG. 1 illustrates various embodiments of a heat sink;

FIG. 2 illustrates various embodiments of a thermal block assembly;

FIG. 3 illustrates various embodiments of a thermoelectric modulecoupled to a heat sink;

FIG. 3 a illustrates various embodiments of an edge heater;

FIG. 4 illustrates various embodiments of a thermal block assemblycoupled to a thermoelectric module and heat sink, and coupled to an edgeheater;

FIG. 5 is a magnified view of a detail of FIG. 4 illustrating variousembodiments of the coupling of the edge heater to the thermal blockassembly and the coupling of the thermal block assembly to thethermoelectric module;

FIG. 5 a is a cross-sectional view of FIG. 5 illustrating variousembodiments of the coupling of the edge heater to the thermal blockassembly and the coupling of the thermal block assembly to thethermoelectric module;

FIG. 6-13 are graph illustrating the temperature curve of the thermalblock assembly and thermal non-uniformity of the thermal block assemblyfor Examples 1-5;

FIG. 14 illustrates various embodiments of a thermoelectric module withdifferent power regions; and

FIG. 15 illustrates various embodiments of a heated cover.

DESCRIPTION OF VARIOUS EMBODIMENTS

Reference will now be made to various embodiments, examples of which areillustrated in the accompanying drawings. Wherever possible, the samereference numbers are used in the drawings and the description to referto the same or like parts.

According to various embodiments, the apparatus for thermally cyclingbiological samples provides heat-pumping into and out of a thermal blockassembly, resistive heating of the thermal block assembly, and diffusivecooling of the thermal block assembly. The term “thermal cycling” orgrammatical variations of such as used herein refer to heating, cooling,temperature ramping up, and/or temperature ramping down. Thermal cyclingduring temperature ramping up, when heating the thermal block assemblyabove ambient (20° C.), can comprise resistive heating of the thermalblock assembly and/or pumping heat into the thermal block assembly bythe thermoelectric module against diffusion of heat away from thethermal block assembly. Thermal cycling during temperature ramping down,when cooling the thermal block assembly above ambient (20° C.), cancomprise pumping heat out of the thermal block assembly by thethermoelectric module and diffusion of heat away from the thermal blockassembly against resistive heating.

According to various embodiments, FIGS. 1-5 and FIGS. 14-15 illustrateportions of an apparatus for thermally cycling biological sample. FIG. 1illustrates heat sink 10, thermal diffusivity plate 12, base plate 14,and fins 16. According to various embodiments, thermal diffusivity plate12 can be separate from the heat sink 10. According to variousembodiments, heat sink 10 can comprise thermal diffusivity plate 12.According to various embodiments, thermal diffusivity plate 12 cancomprise copper. According to various embodiments, base plate 14 andfins 16 can comprise aluminum.

Names of metals as used herein such as copper, aluminum, etc. refer tothe pure metal, alloys of the metal, amalgams of the metal, or anyvariation of the metal known in the art of material science.

According to various embodiments, the thermal diffusivity plate can beconstructed of different material than the rest of the heat sink suchthat the thermal diffusivity plate can have significantly greaterthermal diffusivity than the rest of the heat sink. According to variousembodiments, the base plate and fins can be constructed of differentmaterials. According to various embodiments, the thermal diffusivityplate can comprise other composite materials that provide thermaldiffusivity as known in the art of material science. According tovarious embodiments, as illustrated in FIG. 1, trench 18 can bepositioned around the perimeter of the thermal diffusivity plate and thebase plate. According to various embodiments, trench 18, as illustratedin FIG. 5 a can extend up to the thermoelectric module 30. Trench 18 canlimit the amount of heat diffusion away from the thermal block assemblyand decrease the heat loss from the area bounded by trench 18. Frame 32can be constructed of non-conductive material to avoid substantiallynegating the effect of trench 18.

It can be desirable to reduce the cost and weight of the heat sink whileproviding significantly greater thermal diffusivity with the thermaldiffusivity plate. According to various embodiments, the thermaldiffusivity plate can be constructed of copper and the base plate andfins can be constructed of aluminum because copper can weigh more andcan be more expensive than aluminum. According to various embodiments,the thermal diffusivity plate, base plate, and fins can be constructedof the same material providing similar thermal diffusivity throughoutthe heat sink.

“Thermal diffusivity” or “diffusion” of heat or grammatical variationsof such as used herein refer to the transport property for transientconduction. Thermal diffusivity can measure the ability of a material toconduct thermal energy relative to its ability to store thermal energy.Materials with greater thermal diffusivity can respond more rapidly tochanges in their thermal environment. Thermal diffusivity can becalculated using the formula (1):

$\begin{matrix}{a = \frac{k}{\rho*C_{p}}} & (1)\end{matrix}$

where a is thermal diffusivity which can be measured in square metersper second, k is thermal conductivity which can be measured in watts permeters-Kelvin, C_(p) is specific heat capacity which can be measured injoules per kilograms-Kelvin, and p is density which can be measured inkilograms per cubic meter. As known in the art of material science,there are alternative ways of measuring these thermal properties.

According to various embodiments, the thermal diffusivity plate cancomprise copper, silver, gold, or silicone carbide. “Thermalcapacitance” as used herein refers to the ability of a material to storethermal energy. It can be desirable to provide a thermal block assemblythat can have a significantly lower thermal capacitance so that heatdiffuses to the thermal diffusivity plate. Thermal capacitance can becalculated using the formula (2):

C _(T) =ρ×C _(p)  (2)

where C_(T) is thermal capacitance which can be measured in joules percubic meter-Kelvin, C_(p) is specific heat capacity which can bemeasured in joules per kilograms-Kelvin, and ρ is density which can bemeasured in kilograms per cubic meter. “Significantly” greater or loweras used herein refers to a thermal diffusivity or thermal capacitancevalues of at least twenty-five percent greater or lower than the valuesto which they are compared. Table 1 contains values for each of theaforementioned thermal properties according to various embodiments:

TABLE 1 Thermal Silicone Properties Aluminum Copper Silver Gold MgCarbide k (W/m-K) 209 391 419 301  159 300 C_(p) (J/kg-K) 900 385 234132 1025 640 ρ (kg/m³) 2700  8900  10491  19320  1740 3210  a (m²/s)8.60 × 10⁻⁵ 1.14 × 10⁻⁴ 1.71 × 10⁻⁴ 1.18 × 10⁻⁴ 8.92 × 10⁻⁵ 1.46 × 10⁻⁴C_(T) (J/m³-K) 2.43 × 10⁶   3.43 × 10⁶   2.45 × 10⁶   2.56 × 10⁶   1.78× 10⁶   2.05 × 10⁶  According to various embodiments, a thermal diffusivity plateconstructed of copper, silver, gold, or silicone carbide (for examplesilicone carbide plated by chemical vapor deposition) can havesignificantly greater thermal diffusivity than a base plate and finsconstructed of aluminum or magnesium. According to various embodiments,a thermal diffusivity plate constructed of copper can have asignificantly greater thermal capacitance than a thermal block assemblyconstructed of silver, gold, or magnesium.

According to various embodiments, FIG. 2 illustrates a thermal blockassembly 20 with a plurality of openings 24 and a bottom 22. In thisembodiment, the plurality of openings 24 are adapted to receive samplewells to contain the biological samples. The sample wells can beconfigured into a sample well tray. The top of each sample well can besealed by a cap, an adhesive film, a heat seal, or a gap pad. Accordingto various embodiments, the thermal block assembly can be adapted toreceive and contain the biological sample in a plurality of openings.According to various embodiments, the biological sample can be receivedand contained by surfaces instead of wells. These surfaces can beseparate or integral to the thermal block assembly.

According to various embodiments, the thermal block assembly cancomprise at least one of silver, gold, aluminum alloy, silicone carbide,and magnesium. Other materials known in the art of thermal cycling canbe used to construct the thermal block assembly. These materials canprovide high thermal conductivity.

According to various embodiments, FIG. 3 illustrates the heat sink 10illustrated in FIG. 1 coupled to a thermoelectric module 30. Accordingto various embodiments, thermoelectric module 30 overlaps with thermaldiffusivity plate 12. According to various embodiments, either thethermal diffusivity plate or the thermoelectric module can have a largersurface area. As illustrated in FIG. 3, thermoelectric module 30 sits onprinted circuit board (PCB) 34 and both portions of the thermoelectricmodule 30 are lined by frame 32 that can fill the thermoelectric gapbetween each portion of the thermoelectric module 30 and trench 18.Leads 38 can provide power to the thermoelectric module 30. Gasket 36can be positioned on PCB 34 and can line both the thermoelectric module30 and frame 32. According to various embodiments, the gasket can beconstructed of material comprising at least one of EPDM Rubber, SiliconeRubber, Neoprame (CR) Rubber, SBR Rubber, Nitrile (NBR) Rubber, ButylRubber, Hypalon (CSM) Rubber, Polyurethane (PU) Rubber, and VitonRubber. According to various embodiments, the frame can be constructedof similar material to the gasket, Ultem® Resin (General ElectricPlastics; amorphous thermoplastic polyetherimide), or other suitablematerial. According to various embodiments, frame 32 can be positionedaround the thermoelectric module 30 for alignment with the thermal blockassembly 20 and thermal diffusivity plate 12. According to variousembodiments, the frame can comprise tabs, as illustrated on the cornersof frame 32 in FIG. 3, to facilitate handling of frame 32.

“Thermoelectric module” as used herein refers to Peltier devices, alsoknown as thermoelectric coolers (TEC), that are solid-state devices thatfunction as heat pumps. The Peltier device can comprise two ceramicplates with a bismuth telluride composition in between. When a DCcurrent can be applied heat is moved from one side of the device to theother, where it can be removed with a heat sink and/or a thermaldiffusivity plate. The “cold” side can be used to pump heat out of thethermal block assembly. If the current is reversed the device can beused to pump heat into the thermal block assembly. The Peltier devicescan be stacked to achieve increase the cooling and heating effects ofheat pumping. Peltier devices are known in the art and manufactured byseveral companies, including Tellurex Corporation (Traverse City,Mich.), Marlow Industries (Dallas, Tex.), Melcor (Trenton, N.J.), andFerrotec America Corporation (Nashua, N.H.).

According to various embodiments, FIG. 3 a illustrates an edge heater40. Edge heater 40 can be a resistive heater powered by leads 42illustrated in FIG. 4. According to various embodiments, edge heater 40can be positioned around the perimeter of the thermal block assembly 20such that the edge heater 40 at least partially conforms to the openings24 closest to the perimeter of the thermal block assembly 20. Accordingto various embodiments, an edge heater can be rectilinear withoutconforming to the plurality of openings 24. FIGS. 4-5 illustrate edgeheater 40 coupled to the perimeter of thermal block assembly 20. Edgeheater 40 can be a resistive heater supplied power via leads 42. In thisembodiment, FIG. 5 illustrates the coupling of edge heater 40 to theperimeter of thermal block assembly 20 between the bottom 22 and the top26 of the thermal block assembly 20 and partially around the pluralityof openings 24 that are form the sides of thermal block assembly 20. Theterm “coupled to the perimeter” refers to an edge heater that providesheat from the edges of thermal block assembly. According to variousembodiments, edge heaters can be floating around the perimeter of thethermal block assembly on the sides of the plurality of openings 24, top26 and/or bottom 22. According to various embodiments, edge heater 40 ormultiple heaters can provide different power zones to reduce TNU(thermal non-uniformity) during heating.

According to various embodiments, FIG. 4 illustrates the thermal blockassembly 20 illustrated in FIG. 2 coupled to the thermoelectric module30 and heat sink 10 illustrated in FIG. 3. FIG. 5 illustrates amagnified view of this coupling. According to various embodiments, thethermal block assembly 20 overlaps with thermoelectric module 30 suchthat bottom 22 couples to the surface of thermoelectric module 30.According to various embodiments, either the thermal block assembly 20or the thermoelectric module 30 can have a larger surface area. Seal 44can be positioned over thermal block assembly 20 on top 26 to provide acontrolled environment surrounding the sample well tray (not shown)positioned to fit into the plurality of openings 24 in the thermal blockassembly 20. The seal 44 can reduce the heat diffusion from the thermalblock assembly 20 to the environment surrounding the thermal blockassembly 20. According to various embodiments, the seal can beconstructed of material comprising at least one of EPDM Rubber, SiliconeRubber, Neoprame (CR) Rubber, SBR Rubber, Nitrile (NBR) Rubber, ButylRubber, Hypalon (CSM) Rubber, Polyurethane (PU) Rubber, and VitonRubber.

According to various embodiments, the apparatus for thermal cycling canprovide the top 26 of thermal block assembly 20 access to theenvironment. It can be desirable to protect thermoelectric module 30from moisture in the environment. Seal 44 can provide a connectionbetween the top 26 of the thermal block assembly 20 and a cover (notshown) that provides a skirt down to gasket 36. The cover (not shown)can isolate the components on top of which it is positioned from theenvironment. Seal 44 and/or gasket 36 can provide sealing with orwithout the application of moldable adhesive/sealant, including RTVsilicone rubber (Dow Corning).

According to various embodiments, as illustrated in FIG. 4, clampingmechanism 46 provides pressure to couple thermal block assembly 20 tothermoelectric module 30. The clamping mechanism 46 can be constructedto minimize its contact with the thermal block assembly 20 to avoidsubstantial increase to diffusion of heat. The clamping mechanism 46 canbe constructed of glass filled plastic that has sufficient rigidity toprovide the desired pressure.

According to various embodiments, as illustrated in FIG. 15, a heatedcover 150 can be positioned over the thermal block assembly 20 toprovide heating from above. Heated cover 150 can reduce diffusion ofheat from the biological samples by evaporation by providing recesses156 for the caps (not shown) on sample wells (not shown). Heated cover150 can reduce the likelihood of cross contamination by keeping theinsides of the caps dry, thereby preventing aerosol formation when thesample wells are uncapped. Heated cover 150 can maintain the caps abovethe condensation temperature of the various components of the biologicalsample to prevent condensation and volume loss of the biological sample.Heated cover 150 can provide skirt 158 around the perimeter of platen154. According to various embodiments, the heated cover can be of any ofthe conventional types known in the art. According to variousembodiments, heated cover 150 can slide into and out of a closedposition by manual physical actuation by handle 152. According tovarious embodiments, the heated cover can be automatically, physicallyactuated to and from a closed position by a motor. Heated cover 150comprises at least one heated platen 154 for pressing against the topsurface of the sample well tray. Platen 154 can press down on the samplewell tray so that the sample well outer conical surfaces are pressedfirmly against the plurality of openings 24 in the thermal blockassembly 20. This can increase heat transfer to the sample wells, andcan provide temperature uniformity across sample wells in the samplewell tray similar to the temperature uniformity across thermal blockassembly 20. Platen 154 and skirt 158 can substantially preventdiffusion of heat from thermal block assembly 20. Details of the heatedcovers and platens are well known in the art of thermal cycling.According to various embodiments, the cover can be not heated.

According to various embodiments, FIG. 5 a illustrates a cross-sectionview of edge heater 40 coupled to the thermal block assembly 20 andthermal block assembly 20 coupled to thermoelectric module 30. Thermaldiffusivity plate 12 can be positioned within base plate 14.Thermoelectric module 30 can be coupled to thermal diffusivity plate 12on one side and coupled to thermal block assembly 20 on the other side,powered by lead 38, and lined by frame 32. Thermal block assembly 20 canbe coupled to edge heater 40 at the top surface of bottom 22. Seal 44can be positioned on top 26 of thermal block assembly 20 to line theperimeter of top 26.

According to various embodiments, the thermoelectric module can beconfigured to provide a variety of heat gradients to minimize TNU.Multiple thermoelectric modules can provide a variety of heat gradientsto minimize TNU. According to various embodiments, the thermoelectricmodule 30 can be configured to provide a constant pumping of heat intothermal block assembly 20 by increasing corner heat flux to minimize TNUas described below. According to various embodiments, as illustrated inFIG. 14, thermoelectric module 30 can comprise two or more Peltierdevices that provide different power regions. Leads 38 can providedifferent power to different Peltier devices producing different powerregions. First power region 200 can be coupled to the middle portion ofthe thermal block assembly, while second power region 210 can be coupledto the perimeter of thermal block assembly to compensate for edgeeffect. According to various embodiments, the different power regionscan provide uniform and non-uniform power regions.

According to various embodiments, TNU can be measured by sampling thetemperature at different points on the thermal block assembly. TNU isthe non-uniformity of temperature from place to place within the thermalblock assembly. According to various embodiments, TNU can be measured bysampling the temperature of the sample in the sample well tray atdifferent openings in the thermal block assembly. Actual measurement ofthe temperature of the sample in each well in the sample well tray canbe difficult because of the small volume in each well and the largenumber of wells. Temperature can be measured by any method known in theart of temperature control, including a temperature sensor orthermistor.

According to various embodiments, the components of the thermal cyclingapparatus can be coupled together with thermal interface media,including thermal grease. According to various embodiments, thermalgrease can be positioned at the interface of at least two of the thermalblock assembly, the thermoelectric module, thermal diffusivity plate,and the base plate. Thermal grease can avoid the requirement of highpressure to ensure sufficient thermal contact between components.Thermal grease can provide lubrication between expanding and contractingcomponents that are coupled together to decrease wear on the components.Examples of thermal grease include Thermalcote™ II (Aavid Thermalloy,LLC; k=0.699 W/m-K).

According to various embodiments, methods for thermally cyclingbiological sample can comprise contacting a thermoelectric module to athermal block assembly; heating the thermal block assembly, wherein thethermal block assembly is adapted for receiving the biological sample;and cooling the thermal block assembly, wherein the cooling comprisesdiffusing heat to a heat sink with a thermal diffusivity plate.According to various embodiments, thermally cycling the biologicalsample can comprise contacting said thermal block assembly with an edgeheater, wherein the edge heater is coupled to the perimeter of saidthermal block assembly. According to various embodiments, thermallycycling the biological sample can provide substantial temperatureuniformity to the thermal block assembly. According to variousembodiments, diffusing can provide cooling of at least 10° C. in at mostten seconds for said biological sample. According to variousembodiments, thermally cycling the biological sample can provide heatingand cooling to achieve a PCR cycle time of less than thirty seconds. Forexample, PCR protocols requiring 30 cycles can be completed in less thanfifteen minutes. Various PCR protocols are known in the art of thermalcycling and can include maintaining 4° C. per second temperature rampingup or ramping down.

EXAMPLES

According to various embodiments, the thermal block assembly is heatedby ramping up the set point on the temperature controller for thethermal block assembly and is cooled by ramping down the set point onthe temperature controller. Following are several examples whosetemperature curves are illustrated in FIGS. 6-13. In FIGS. 6-13, the setpoint temperature curve 60 is associated with the scales on the leftvertical axis of the graph indicating temperature in degrees Centigradeand the horizontal axis indicating time in seconds. The time frame inFIGS. 6-13 is an arbitrary block of time in a thermal cycling protocol.In FIGS. 6-13, the thermal non-uniformity curves are associated with thescales on the right vertical axis of the graph indicating TNU in degreesCentigrade and the horizontal axis indicating time in seconds.

Comparative Example 1 Thermal Diffusivity Plate

In Example 1, a thermal diffusivity plate constructed of 99.9% EDMcopper having a thickness of 8.0 millimeters was coupled to a base plateand pin fins constructed of 6063-T5 aluminum having a thickness of 5.0millimeters. A thermal block assembly constructed of silver plated withgold was coupled to a thermoelectric device constructed of bismuthtelluride. The thermoelectric device was coupled to the thermaldiffusivity plate. An edge heater having a power output of 9.3 Wattsmanufactured by Minco Products, Inc. (Minneapolis, Minn.) was coupled tothe thermal block assembly. A seal constructed of silicone rubber waspositioned on the top of thermal block assembly. This thermal cyclingapparatus was compared to a thermal cycling apparatus similar to the onedescribed above except that the thermal diffusivity plate was replacedwith a base plate having a thickness of 13.0 millimeters. FIG. 6illustrates the temperature curve and TNU curves of the thermal blockassembly for ramping up temperature. FIG. 7 illustrates the temperaturecurve and TNU curves for ramping down temperature. In FIGS. 6-7, the TNUcurve 62 relates to the thermal cycling apparatus with the thermaldiffusivity plate and TNU curve 64 relates to the thermal cyclingapparatus without a thermal diffusivity plate.

Comparative Example 2 Pin Fin and Swage Fin

In Example 2, a thermal cycling apparatus with a thermal diffusivityplate similar to the one described in Example 1 was modified to replacethe pin fin heat sink with a swage fin heat sink. The thermal cyclingapparatus with a thermal diffusivity plate and swage fins was comparedto a similar thermal cycling apparatus except that the thermaldiffusivity plate was replaced with a base plate having a thickness of13.0 millimeters. FIG. 8 illustrates the temperature curve and TNU ofthe thermal block assembly for ramping up temperature. FIG. 9illustrates the temperature curve and TNU of the thermal block assemblyfor ramping down temperature. In FIGS. 8-9, the TNU curve 82 relates tothe thermal cycling apparatus with a swage fin heat sink and a thermaldiffusivity plate and TNU curve 84 relates to the thermal cyclingapparatus with a swage fin heat sink without a thermal diffusivityplate.

In Examples 1 and 2, as illustrated by FIGS. 6-9, a thermal diffusivityplate can reduce the TNU during thermal cycling whether a pin fin orswage fin heat sink diffuses heat away from the thermal diffusivityplate. This can be demonstrated by the TNU curves, i.e., TNU curves 62and 82 reach lower TNU values than TNU curves 64 and 84 after the setpoint temperature curve 60 reaches the set point near the 20 second markin FIGS. 6-9.

Comparative Example 3 Multiple Edge Heaters

In Example 3, a thermal diffusivity plate constructed of 99.9% EDMcopper having a thickness of 8.0 millimeters was coupled to a base plateand fins constructed of 6063-T5 aluminum having a thickness of 5.0millimeters. A thermal block assembly constructed of silver plated withgold was coupled to a thermoelectric device constructed of bismuthtelluride. The thermoelectric device was coupled to the thermaldiffusivity plate. An edge heater having a power output of 9.3 Wattsmanufactured by Minco Products, Inc. (Minneapolis, Minn.) was coupled tothe thermal block assembly. A seal constructed of silicone rubber waspositioned on the top of thermal block assembly. This thermal cyclingapparatus was compared to a thermal cycling apparatus similar to the onedescribed above except that more than one edge heaters was coupled tothe thermal block assembly. FIGS. 10-11 illustrate the temperature curveand TNU of the thermal block assembly of varying edge heaters withdifferent fin configurations during thermal cycling. FIG. 10 illustratesa comparison between one and two edge heaters with a pin fin heat sink.TNU curve 102 relates to the thermal cycling apparatus with one edgeheater and TNU curve 104 related to the thermal cycling apparatus withtwo edge heaters. FIG. 11 illustrates a comparison between one and threeedge heaters with a swage fin heat sink. TNU curve 112 relates to thethermal cycling apparatus with one edge heater and TNU curve 114 relatesto the thermal cycling apparatus with three edge heaters.

Example 3 illustrates that an increased edge heating reduces TNU inheating cycles whether a pin fin or swage fin heat sink diffuses heataway from the thermal diffusivity plate. In the swage fin configuration,additional heat provided by the edge heater during heating increased theTNU during cooling.

Comparative Example 4 Seal

In Example 4, a thermal diffusivity plate constructed of 99.9% EDMcopper having a thickness of 8.0 millimeters was coupled to a base plateand pin fins constructed of 6063-T5 aluminum having a thickness of 5.0millimeters. A thermal block assembly constructed of silver plated withgold was coupled to a thermoelectric device constructed of bismuthtelluride. The thermoelectric device was coupled to the thermaldiffusivity plate. A seal constructed of silicone rubber was positionedon the top of thermal block assembly. The thermal cycling apparatusdescribed above was compared to a thermal cycling apparatus similar tothe one described above except that the seal was removed. FIGS. 12-13illustrate the temperature curves and TNU curves of the thermal blockassembly with a thermal diffusivity plate during thermal cycling. FIG.12 related to ramping up temperature to the thermal block assembly andFIG. 13 related to ramping down temperature to the thermal blockassembly. In FIGS. 12-13, TNU curve 122 relates to the thermal cyclingapparatus with a silicon rubber seal and TNU curve 124 relates to thethermal cycling apparatus without a silicon rubber seal.

Example 4 illustrates that a silicon rubber seal can provide a barrierto condensation without significantly affecting the TNU change in athermal cycling apparatus with a thermal diffusivity plate and pin finheat sink.

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing quantities, percentages orproportions, and other numerical values used in the specification andclaims, are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending upon thedesired properties sought to be obtained by the present invention. Atthe very least, and not as an attempt to limit the application of thedoctrine of equivalents to the scope of the claims, each numericalparameter should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass any and all subranges subsumedtherein. For example, a range of “less than 10” includes any and allsubranges between (and including) the minimum value of zero and themaximum value of 10, that is, any and all subranges having a minimumvalue of equal to or greater than zero and a maximum value of equal toor less than 10, e.g., 1 to 5.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the,” include plural referents unlessexpressly and unequivocally limited to one referent. Thus, for example,reference to “a thermoelectric module” includes two or morethermoelectric modules.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to various embodimentsdescribed herein without departing from the spirit or scope of thepresent teachings. Thus, it is intended that the various embodimentsdescribed herein cover other modifications and variations within thescope of the appended claims and their equivalents.

1. An apparatus for thermally cycling biological samples comprising: athermal block assembly for receiving said biological samples; athermoelectric module coupled to said thermal block assembly; and a heatsink, wherein said heat sink is coupled to said thermoelectric modulewith a thermal interface medium, wherein said heat sink comprises a baseplate, fins, and a thermal diffusivity plate, and wherein said thermaldiffusivity plate comprises a different material than said base plateand fins, wherein said thermal diffusivity plate provides substantialtemperature uniformity to said thermal block assembly during thermalcycling.
 2. The apparatus of claim 1, wherein said thermal diffusivityplate is positioned to couple to said thermoelectric module with thethermal interface medium.
 3. The apparatus of claim 1, wherein saidthermal block assembly comprises at least one of silver, gold, aluminum,silicone carbide, and magnesium.
 4. The apparatus of claim 1, whereinsaid base plate and fins comprise aluminum.
 5. The apparatus of claim 1,wherein said thermoelectric module comprises a thermoelectric gap,wherein said thermoelectric gap provides substantial temperatureuniformity throughout said thermal block assembly.
 6. The apparatus ofclaim 5, wherein said thermoelectric gap is less than 5 millimeters. 7.The apparatus of claim 1, further comprising an edge heater, whereinsaid edge heater is coupled to the perimeter of said thermal blockassembly.
 8. The apparatus of claim 1, wherein said apparatus provides aPCR cycle time of less than thirty seconds.
 9. An apparatus forthermally cycling biological samples comprising: a thermal blockassembly for receiving said biological samples; a thermoelectric modulecapable of heating and cooling, wherein the thermoelectric module iscoupled to said thermal block assembly; a heat sink; and a thermaldiffusivity plate comprising copper coupled to said thermoelectricmodule with a thermal interface medium and coupled to said heat sink,wherein said thermal diffusivity plate is positioned between saidthermoelectric module and said heat sink and has a significantly greaterthermal diffusivity than said heat sink, and provides substantialtemperature uniformity to said thermal block assembly during thermalcycling.
 10. The apparatus of claim 9, wherein said substantialtemperature uniformity provides cooling of at least 10° C. in at mostten seconds for said thermal block assembly.
 11. The apparatus of claim9, wherein said thermal block assembly comprises silver and gold. 12.The apparatus of claim 9, wherein said thermoelectric module comprises athermoelectric gap, wherein said thermoelectric gap provides substantialtemperature uniformity throughout said thermal block assembly.
 13. Theapparatus of claim 12, wherein said thermoelectric gap is less than 5millimeters.
 14. The apparatus of claim 9, further comprising an edgeheater, wherein said edge heater is coupled to the perimeter of saidthermal block assembly.
 15. The apparatus of claim 1, wherein saidthermoelectric module comprises at least two power regions.
 16. Theapparatus of claim 1, further comprising a seal positioned on top ofsaid thermal block assembly.
 17. The apparatus of claim 1, wherein thethermal interface medium is thermal grease.
 18. An apparatus of claim 1,wherein said thermal diffusivity plate is positioned within said baseplate.
 19. An apparatus of claim 1, wherein said thermoelectric module'shorizontal surface area overlaps said thermal diffusivity plate'shorizontal surface area.
 20. An apparatus of claim 19, wherein saidthermoelectric module's horizontal surface area is larger than saidthermal diffusivity plate's horizontal surface area.
 21. An apparatus ofclaim 19, wherein said thermal diffusivity plate's horizontal surfacearea is larger than said thermoelectric module's horizontal surfacearea.
 22. An apparatus of claim 9, wherein said thermal interface mediumis thermal grease.
 23. An apparatus of claim 9, wherein saidthermoelectric module's horizontal surface area overlaps said thermaldiffusivity plate's horizontal surface area.
 24. An apparatus of claim23, wherein said thermoelectric module's horizontal surface area islarger than said thermal diffusivity plate's horizontal surface area.25. An apparatus of claim 23, wherein said thermal diffusivity plate'shorizontal surface area is larger than said thermoelectric module'shorizontal surface area.
 26. An apparatus of claim 9, wherein saidthermal diffusivity plate is positioned within a base plate of said heatsink.